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Comments Prepared by Maryland Department of the Environment (MDE) 

On Sierra Club’s May 4, 2015, “Evaluation of Compliance with the 1-hour NAAQS for SO2” for

C.P. Crane Generating Station and Fort Smallwood Complex (Brandon Shores & H.A. Wagner), Maryland 

On behalf of Sierra Club, Wingra Engineering conducted modeling of the Fort Smallwood Complex (Wagner & 

Brandon Shores Generating Stations) and Crane Generating Station with the most current (2012-14) meteorological 

data using U.S. EPA’s regulatory model, AERMOD Ver. 14134. The modeling used both allowable and maximum 

emissions rates limits from the permit application and actual hourly emission rates (CEMS data) to conduct the 

1-hour SO2 NAAQS (196.2 ug/m3

) modeling. 

MDE has taken this opportunity to review and prepare comments on the 1-hour SO2 modeling conducted by Sierra 

Club. The comments are as follow: 

1. Sierra Club has modeled 1-hour SO2 using AERMOD and AERMET Ver. 14134. U.S. EPA’s latest 

version, 15181, of AERMOD and AERMET has been available since June 30, 2015. MDE would 

recommend designation modeling using latest version of AERMOD/AERMET for this modeling analysis. 

2. Sierra Club has modeled the Wagner and Brandon Shores Generating Stations as a single complex, the 

Fort Smallwood Complex. MDE recommends modeling Brandon Shores and Wagner separately. 

3. Sierra Club’s modeling includes allowable emission rate limits and actual hourly emission rates. Sierra 

Club has also modeled the Crane, Wagner and Brandon Shores Generating Stations using the “maximum” 

emission rate. In MDE’s opinion, these “maximum” values do not reflect the accurate operating scenarios 

of the facilities or the probable conditions (startup, shutdown, maintenance, etc.) under which such higher 

emissions are released from the units. Since the 1-hour SO2 NAAQS is statistical in nature, the predicted 1-

hour SO2 modeling results will have a higher degree of uncertainty. 

4. Sierra Club’s modeling did not include the effects of building downwash (BPIP program) and GEP height 

of the stacks. It is a well known fact that inclusion of building dimensions and parameters in the modeling 

affects the downwind concentrations. MDE would recommend that building downwash be used in the 

modeling analysis. 

5. In the modeling, Sierra Club has set the flag pole to receptors and placed the receptors over the water 

bodies. However, EPA’s SO2 NAAQS Designations Modeling Technical Assistance Document (TAD) 

recommends the designation modeling without receptors over water bodies, and predicted concentrations 

at the ground levels, i.e., without flag pole receptor heights. 

6. Background concentrations used in the modeling by Sierra Club are the Howard University (HU)-

Beltsville monitoring site for years 2012-14. The background concentration of 26.2 μg/m3

 is based on Tier 

1 analysis, based on EPA’s 1-hour SO2 Modeling TAD. 

7. Sierra Club’s modeling did not include the cause-and-contribute (MAXDCONT) analyses. MDE believes 

that such runs/files/analyses are helpful in evaluating the impacts of affected sources in the area. These 

analyses are beneficial in sources interactive study, and quantifying the concentrations by sources/units at 

the receptors.